Paint filter



Dec. 21, 1965 E. T. NORID ETAL PAINT FILTER Original Filed Maren 14,1960 P i 5 mww Jw TA M W /7f V2 Q/W/ m N IL I United States Patent3,2245% PAINT FILTER Eric T. Nerd, Uherlin, and Samuel R. Rosen, Lorain,@hio, assignors to Nordson (Iorporation, Amherst, @hio, a corporation ofOhio Continuation of application Ser. No. 14,893, Mar. 14, 1960. Thisapplication Nov. 26, 1962, Ser. No. 241,463 4 Elaims. (Cl. 210-438) Thisapplication is a continuation of our co-pending application Serial No.14,893, filed March 14, 1960, and now abandoned.

This invention relates to pain filters and particularly to filterssuitable for use in filtering paint under high pressure or hightemperature of both. For convenience, we shall use the word paint in itspresent comprehensive and conventional meaning in this art to comprehendpainting. coating and finishing materials in general, including enamels,emulsions, slurries and suspensions, catalyzed resins, mastics andasphaltums, waxes and paraffins, oils and lubricants, lacquers,plastisols, adhesives and other specialty coatings.

Prior paint filters and, particularly, prior high pressure paint filtershave been based on and designed to operate according to the old andwell-known settling method of dealing with sediment and the like,filtered from a liquid. Such filters broadly comprise a settlingchamber, an inlet and an outlet at or near the top of the chamber and afiltering element located ahead of the outlet and through which thepaint to be filtered is forced to pass. conventionally, the filteringelement of such filters may take the form of a cylindrical screen, or acylindrical pile of thinly spaced washers, whose axial dimension isseveral times greater than its diameter. These filters extendedvertically down into and were surrounded by the settling chamber. Thefluid to be filtered was introduced into the top of the settling chamberat a point radially outside of and surrounding the cylindrical filteringelement and passed radially through the screen of the element fromwhence it is generally conducted axially upwardly and internally of thecylindrical filtering element to an outlet, the material to be separatedfrom the filtered fluid being separated on the radially outer surface ofthe screen or pile. This arrangemnet permits and is designed toencourage the relatively undisturbed settling of sediment and particlesremoved from the paint into the lower portion of the settling chamber.

A point of difficulty in the operation of a conventional prior artsettling type filter is at the upstream and/ or lower side of the filterelement or screen. During the operation of the filter, material removedfrom the fluid being filtered accumulates in the settling chamber. Inaddition, pigment settles out of the paint and tends to accumulate inthe settling chamber when the flow of paint through the filter isreduced or stopped. The accumulated material in the settling chambertends to form a semi-hardened mass of material which, if notperiodically removed, will eventually build up and block a portion ofthe filtering area of the filter element extending into the settlingchamber. A blowdown or drain-off valve at the bottom of the settlingchamber may or may not be effective to remove the sediment if it is nottoo caked. Even when such a valve is provided, however, it is frequentlynecessary to disassemble the filter and mechanically remove theaccumulation of separated material and caked pigment from the lowerportion of the settling chamber and the filtering element.

The prior art filters are also subject to other operationaldisadvantages. For instance, when paint flow through the filter isreduced or stopped, pigment tends to settle out of suspension by gravityonto the downstream side of the filtering element where it tends tostick together and to Ice the filter element and form a semi-hardenedmass. Upon a subsequent increase in the rate of flow of paint throughthe filter, this mass of settled pigments may break loose and break upand be carried through the rest of the system into the orifices, areasor channels which the filter is supposed to be protecting. On the otherhand, this mass always reduces the capacity of the filter and tends toend its usefulness.

A general object of our invention is to provide a selfcleaning filterespecially adapted to filter hot paint under high pressure, and which,with-all, is small in relation to its capacity, light in weight andrugged in structure, adapted to withstand thermal expansion andcontraction, as well as, and/or simultaneously with, great changes inpressure or under high pressure.

A specific object is to eliminate settling chambers in paint filtersstructurally and/ or functionally and eliminate the problems inherenttherewith and incident thereto. Another and more general object is tosolve the problems that have heretofore plagued the prior art of hotpaint filters including those mentioned and referred to above.

One of the objects of our invention, therefore, is to provide anefiective paint filter which does not permit the formation ofaccumulations of separated material and/ or paint pigment tending toreduce the efficiency of the filter. A particular object is to provide apaint filter which prevents the accumulation on the downstream side ofthe filtering element of pigment that may settle out of the paint duringperiods of reduced or no flow through the filter. A specific object ofour invention is to provide a paint filter which acts to prevent theaccumulation and formation into a semi-hardened mass of the materialseparated from the paint by the filter and pigment that may settle outof the paint on the upstream side of the filtering element. A furtherobject is to provide a paint filter of simple construction having aminimum number of parts that are easily assembled, disassembled,cleaned, repaired, obtained and replaced. Yet another object is toprovide a simple and effective seal between the necessarily separableouter parts of the filter.

Briefly, we accomplish these, and other objects that will appear as thisdescription proceeds, by departing from the widely accepted settlingmethod of dealing with the mateerial separated by, at or in the filter.A preferred form of filter embodying our invention is described below inconnection with the accompanying drawings in which:

FIGURE 1 is a side elevation of our filter in assembled condition andshowing the filter base and shell in section and the internally locatedfiltering element and the combined tie bolt and outlet channel inpartial section;

FIGURE 2 is an enlarged cross section through the filtgr taken along theline 22 as shown in FIGURE 1; an

FIGURE 3 is a side elevation of the tie bolt removed from the filter.

In its preferred form and as seen in FEGURE 1, our filter comprises abase it) having an inlet 11 and outlets l2. and 13, a cylindrical shell14 having a straight side wall 15 and a closed upper end wall 16 andhaving its lower open end fitted to the base ll Our filter alsocomprises a cylindrical filtering element or screen 17 having both endsopen and a combined tie bolt and outlet conduit 18 which acts to holdthe various elements of the assembled filter together. The top face ofbase HP is provided with an annular groove 2% adapted to receive theannular open end of shell 14. In order to obtain a satisfactory seal,the external annular surface of cylindrical shell 14 adjacent its openend is tapered inwardly toward the open end as at 21 and that portion ofthe radially outward wall 22 of annular groove 2t} is tapered acomplementary amount as at 23 so as to match and engage the taper on theend of cylindrical shell 14.

This structure acts to seal the joint between the shell 14 and baseunder conditions of widely varying pressure and temperature in a mannerdescribed below.

A central, vertical, partially tapped bore 1225 is provided through base10 concentric with annular groove 20 comprising the lower outlet portion12 and the upper threaded portion 25. Above and beyond the tappedportion 25, the bore is counterbored and enlarged as at 26 with aradially extending internal shoulder 27 proximate the upper ends of thethreads of the bore 25. A threaded inlet port 11 in base 10 communicateswith the interior of cylindrical shell 14 byrneans of a vertical passage29, see also FIG. 2, connecting inlet 11 with the bottom of annulargroove 20. To accommodate blow-down and/or drain-off, we provide aseparate vertical passage 31, see also FIG. 2, preferably larger thanthe passage 29 and also communicating with the interior of cylindricalshell 14 via the bottom of annular groove 20 and having a threadedoutlet port 13. An appropriate plug or valve, not shown, may be screwedinto the outlet 13 to close the same under normal or usual operation ofthe filter, and to permit drainage or blow-down whenever desired.

The upper-end wall 16 in cylindrical shell 14 is provided with acentrally located bore 33. The outer end of bore 33 is reamed andtapered as at 34 and the inner end is counterbored and enlarged as at 35and has a radially extending shoulder 36, vis-a-vis the shoulder 27 ofthe base 10.

The filtering element 17 has an exterior cylindrical screen portion 37with upper and lower annular end bearing rings 38 and 39 which have aninternal diameter adapted to closely receive the ends of the screen; therings 38 and 39 overlying the ends of the screen cylinder 37 and beingattached thereto as by brazing to form axial and radial bearing surfaceson each end of the screen. The outside diameter of bearing ring 38 fitsthe counterbore 35 with a snug fit. The inside diameter of bearing ring38 with screen cylinder 37 brazed therein substantially matches, and ispreferably no smaller than the inside diameter of hole 33 when the axialend of bearing ring 38 abuts the shoulder 36. Bearing ring 39 issimilarly received in the counterbore 26 of bore 25 in base 10. Thelength of screen cylinder 37 is such that the axial ends of the twobearing rings 38 and 39 are firmly abutted against shoulders 36 and 27,respectively, when the paint filter is assembled as shown in FIGURE 1.

Tie bolt 18, see FIG. 3, has an internal bore 41 extending from itslower externally threaded end 25a up to, but not through its hex headportion 42. The bolt 18 passes through the central bore 33 in the topclosure 16 of shell 14 and engages tapped bore 25 in base 10 and acts intension to tighten down the shell 14 into the annular taper 23. Belowthe head 42, tie bolt 18 is provided with a tapered annular surface 44which matches and engages taper 34 on the outer end of bore 33 to effecta fluid-tight seal of bore 33 against loss of internal fluid pressurewithin shell 14 during operation of the paint filter. That portion oftie bolt 18 passing through cylinder screen 37 is externally fluted withcircumferentially spaced axially extending ribs 46 freely slidablewithin and engaging the interior of the cylinder screen 37 andsupporting the screen against deformation or collapse. External axialgrooves 47 lie between ribs 46 on the outside of bolt 18 and on thedownstream side of screen cylinder 37, and communicate with each otherat their ends where ribs 46 are cut off and terminate in annular grooves48. A number of radially directed holes 49 connect the grooves 47 and 48with central bore 41 of the tie bolt. The ribs 46 back up and preventdeformation and collapse of cylinder screen 37 under endwise compressionbetween the shoulders 27 and 36 and under adverse operating conditions.The grooved passages 47 and 48, together with holes 49 collect anddirect the filtered material from the downstream side of screen 37 tocentral bore 41 of tie bolt 18 which is in communication with outlet 12at the bottom of the filter.

A feature of our invention is the facility with which the filter screen37 with its terminal rings 38 and 39 may be stripped from the fluted tiebolt 18 wherewith to separate these two constituent elements of ourfilter when the same are sought to be inspected, cleaned, replaced and/or repaired. When the parts are assembled in their operative relation asshown in FIG. 1, then if the tie bolt be unscrewed from the base whilethe shell 14 is held in approximately its normal fixed relation to thebase as shown in FIGURE 1, the bolt will thereupon be screwed back,upwardly and outwardly of the screen as well as out of the end closure16 of the shell 14. When the threads 25-25a have become disengaged, thebolt 18 may then be drawn upwardly as viewed in FIGURE 1 out of theshell and out of the filter screen, leaving the screen in approximatelythe position shown in FIG. 1 with, however, the tie bolt removed; theseating of the upper ring 38 in the counterbore 35 retaining the screeninside of the filter shell while the tie bolt is stripped from withinthe interior thereof. Thereafter, manual removal of the shell 14 fromthe base 10 will disconnect one end or the other of the screen eitherfrom the base or from the closure of the shell and leave the screen in aposition for manual removal from whichever of the counterbores 26 or 35with which the screen may have remained in engagement. Alternatively,the shell, bolt and filter screen may be unscrewed together from thebase and the bolt may then be stripped upwardly from within the screenas mentioned above, or the screen may be stripped off the bolt while thebolt continues its engagement with the closure on the tapered surfaces3444. The facility with which the screen may be stripped from the boltis a matter of significant convenience and also serves to preserve thescreen from injury that might befall it under less propitiousconditions.

In operation, the filter is assembled as shown in FIG- URE 1 with inlet11 connected to a paint or fluid supply under pressure, not shown, andoutlet 12 connected to the system, hose, conduit or gun which is to besupplied with the filtered paint or fluid. Outlet 13 is normally closedby a plug, drain-off or blow-down valve. Unfiltered paint under pressureenters the filter through inlet 11 and flows upwardly into shell 14through passage 29 and between side wall 15 of the shell 14 and theoutside or upstream side of screen 37 of filtering element 17. Under theinfluence of system pressure, the fluid is forced radially throughfilter element 17 from the upstream to the downstream side ofcylindrical screen 37. The material too large to pass through the screenis separated from the fluid on the upstream side of the screen 37 whilethe filtered fluid that has passed through the screen flows alongpassages 47 and 48 and radially through holes 49 into the central bore41 of tie bolt 18. The filtered fluid flows downwardly in bore 41 andout of the lower end of tie bolt 18 through outlet 12. Substantially allthe filtered paint is required to flow downwardly and out of the filterpromptly and directly after being filtered through the screen 37 andgiven no place and little time to effect sedimentation or deentrainmentof any part or constituent on the downstream side of the screen in thefilter. On the upstream side of the screen, the incoming upwardlydirected flow of paint tends to forever wash the screen and preventadhesion thereto of Waste and filtered-out material, and also agitatesand disperses filtered-out substances and impurities from accumulatingin the bottom of the filter chamber between the screen and the shellnear the inlet 29. By the same token and effect, the waste andimpurities are given substantially no rest or refuge in the filterchamber other than near the blow-down Outlet 31 and in that outlet or inthe conduit leading from the outlet to the blow-down valve. Another ofthe accomplishments of our invention is to free the filter screen andfilter chamber from accumulated waste and place it where it can beeasily and largely removed by simple outflow through the waste outlet.

During operation, our filter is expected to be subjected to highinternal fluid pressures and high temperatures. For example, thepreferred embodiment of our invention is often and successfully used insystems operating at from about 500 to 1000 pounds per square inch andwith fluid temperatures exceeding 300 F. Under such conditions, the tiebolt 18 cooperates with the novel seal of our invention to preventleakage between the shell 14 and the base 10. The tie bolt 18 isnormally drawn up tightly so that the surfaces of the two tapers 34 and44 at the top of shell 14 and the upper end of tie bolt 18,respectively, and the surfaces of tapers 22 and 23 of shell 14 and base10, respectively, are in fluid-tight sealing engagement with each other.The high pressure acting internally of the filter against closure 16tends to force the surface of female taper 34 at the top of cylindricalshell 14 into tighter sealing engagement with the surface of male taper44 on tie bolt 18. The high internal pressure thus also places thatportion of tie bolt 18 below taper 44 in tension tending to stretch thebolt and, axially displace the surface of taper 21 on the bottom ofshell 14 away from the surface of taper 23 on base 10. However, thefluid-tight seal between surfaces of tapers 21 and 23 is not impaired inspite of axial displacement due to elongation of tie bolt 18, becausethe internal pressure within the shell tends to increase the diameterthereof in at least the region of reduced wall thickness at and near thetaper 21 whereby to hold the outer surface of taper 21 in sealingengagement with the surface of taper 23. Thus, the seal between theshell 14 and the base is accomplished by making the joint therebetweenon a long, gentle, axial taper and by making the wall thickness of theshell 14 thin enough, consistent with strength to resist bursting, toyield an increase in diameter of the shell great enough to maintain afluidtight seal beween the contacting surfaces while the shell 14 isdisplaced axially away from the base because of the elongation of tiebolt 18. In this connection, we prefer to use an axial taper ofapproximately 10. That is to say: we keep the tapered joint 21-23fluid-tight against high fluid pressure by balancing diametric expansionof the shell against stretch of the tie bolt. Additionally, the seal21-23 accommodates differences in longitudinal expansion of the shelland tie bolt and changes in circumferential dimension between shell 14and annular groove due to temperature changes.

From the foregoing description of structure and operation of a preferredembodiment, it will be apparent that our invention overcomes theundesirable settlement of pigment or other paint constituents out ofsuspension into the downstream side of the filtering wall or screen byavoiding traps and resting places on the downstream side of the screenand by locating the outlet from the filter at the bottom of and in theaxis of outflow from the filtering screen. There is no place in ourfilter for pigment or other parts of the filtrate to settle out and/oraccumulate on the downstream side of the filtering screen except in theou et passage from the filter whence it is carried off and along in thedownstream channels where flow and agitation tend to entrain orreentrain it in or into the paint strea-m. Because the pigment and otherdeentrainable parts of the filtrate cannot settle out of the paintoutside of the stream of flow from the filter, they cannot accumulatesufliciently to form any compact or semi-hardened mass as they do insettling type filters.

The problem of build-up of accumulated separated material and the likein the bottom of the settling chamber around the outside of the upstreamside of the filtering element is effectively solved by our invention bythe elimination of settling chambers as previously known; that is, onein which settling is permitted, undistributed and unagitated by the flowof fluid through the system. In our filter the incoming fluid enters thefluid chamber at the bottom and is directed upward along the outersurface of the filtering screen. The flow of fluid in this case tends tocontinuously agitate the separated waste and impure materials. This flowprevents the separated material from packing and forming any compact andsemi-hardened mass removed from the path of waste removal through theblowdown valve or waste discharge orifice.

Any air that might otherwise tend to be trapped in the top of the filterchamber is entrained in the fluid stream and evacuated from the chamberand carried away through the filtrate outlet 12 of the filter. Itappears that this desirable result is aided and/or affected by theprojection of the incoming fluid upwardly and parallel with thefiltering screen, particularly when high pressure is employed in thefilter. We prefer to have the small intake opening 29 point intocylindrical shell 14 from base 10 in order to get a high velocity flowor jet into the filter chamber between the shell and the screen. We alsoprefer that the filter chamber be rather narrow and elongated in orderto give vigorous turbulent motion to all the paint therein, includingthe top part of the shell where air might otherwise tend to be trapped.

Further, our invention provides a fluid-tight seal without the aid ofO-rings or other sealing elements between the cylindrical shell and thebase of the filter where there must be a detachable connection to permitassembly, cleaning and replacement of parts. The taper seal 21-23 alsopermits the desirable result of holding the working parts of the filtertogether and maintaining a fluid seal between them by the use of asingle bolt even while the bolt is elongated by tension and/ or thermalexpansion.

Changes, modifications and improvements may be made to theabove-described preferred form of our invention without departing fromthe precepts and principles of our invention and the essential teachingsof this specification. Therefore, we do not wish our patent to belimited to the particular form of our invention herein specificallyillustrated and described nor in any manner inconsistent with theprogress by which our invention has promoted the art.

We claim:

1. A paint filter comprising a ported base and a hollow cylindricalpressure vessel with a vertical axis mounted above and upon said portedbase,

said base having a smooth, upwardly facing, female, conical metalsurface with its axis coincident with the said axis of said vessel, and

said vessel having its upper end closed and having an open substantiallycircular lower end, said lower end being diametrically expansible underfluid pressure and being yieldable with respect to its circular form,

said lower end of said vessel having a smooth metal male surfacecooperative with and entering and engaging said female surface andhaving exclusive metal-to-metal, sliding and sealing contact therewith,

said base having a paint inlet port and a paint outlet portcommunicating with said vessel adjacent said lower end of the vessel,

filtering means disposed in said vessel across the path of paint flowthrough said vessel from said inlet port to said outlet port,

a tension member having an axis substantially co incident with said axesand acting between the upper end of said vessel and said base andholding said male surface of said lower open end of said vessel influid-tight, slidable, sealing engagement with said female surface ofsaid base portion,

the angle of pitch of said conical female surface of said base withrespect to the axis thereof being no greater than the angle at whichsealing contact would tend to be lost between said surfaces when saidtension member is stretched axially and said male surface is movedaxially upwardly and expanded radially outwardly by the pressure offluid in said vessel,

metal-to-metal sealing engagement being maintained between said male andfemale surface irrespective of relative movement therebetween due tochanges in fluid pressure in said vessel.

2. The paint filter according to claim 1 in which said filtering meanshas an axis coincident with said axis and has a hollow cylindrical endportion, and

said base and the said closed end of said vessel have means engaging andpositioning said filtering means,

said filter engaging means and said filtering means having an axiallysliding fit at said hollow cylindrical end portion to maintainengagement therebetween irrespective of relative movement between saidbase and the said upper end of said vessel due to changes in fluidpressure in said vessel.

3. The paint filter of claim 1 in which the said male surface of thesaid lower end of said vessel is conical and substantially coextensivewith the said female surface of said base when said vessel is stressedby fluid pressure therein.

4. A paint filter according to claim 1 in which said filtering meanscomprises an axially straight cylindrical pervious wall within andcoaxial with said vessel having interior communication with said outletport, and

being laterally spaced away from the interior surface of said vessel,and

forming an axially straight-walled, trap-free chamber therebetween, andin which said paint inlet port opens to said chamber radially outwardlybeyond the radial extent of said filtering means, and

projects paint directly at the upper end of said vessel for agitatingpaint in said chamber, and for washing said wall.

References Cited by the Examiner UNITED STATES PATENTS 1,940,923 12/1933Stringer 2l0442 X 2,389,431 11/1945 Hallinan 210-440 X 2,554,748 5/1951Lewis et a1. 210-440 X 2,747,744 5/1956 Gretzinger 210442 REUBENFRIEDMAN, Primary Examiner.

HARRY B. THORNTON, Examiner.

1. A PAINT FILTER COMPRISING A PORTED BASE AND A HOLLOW CYLINDRICAL PRESSURE VESSEL WITH A VERTICAL AXIS MOUNTED ABOVE AND UPON SAID PORTED BASE, SAID BASE HAVING A SMOOTH, UPWARDLY FACING, FEMALE, CONICAL METAL SURFACE WITH ITS AXIS COINCIDENT WITH THE SAID AXIS OF SAID VESSEL, AND SAID VESSEL HAVING ITS UPPER END CLOSED AND HAVING AN OPEN SUBSTANTIALLY CIRCULAR LOWER END, SAID LOWER END BEING DIAMETERICALLY EXPANSIBLE UNDER FLUID PRESSURE AND BEING YIELDABLE WITH RESPECT TO ITS CIRCULAR FORM, SAID LOWER END OF SAID VESSEL HAVING A SMOOTH METAL MALE SURFACE COOPERATIVE WITH AND ENTERING AND ENGAGING SAID FEMALE SURFACE AND HAVING EXCLUSIVE METAL-TO-METAL, SLIDING AND SEALING CONTACT THEREWITH, SAID BASE HAVING A PAINT INLET PORT AND A PAINT OUTLET PORT COMMUNICATING WITH SAID VESSEL ADJACENT SAID LOWER END OF THE VESSEL, FILTERING MEANS DISPOSED IN SAID VESSEL ACROSS THE PATH OF PAINT FLOW THROUGH SAID VESSEL FROM SAID INLET PORT TO SAID OUTLET PORT, A TENSION MEMBER HAVING AN AXIS SUBSTANTIALLY COINCIDENT WITH SAID AXES AND ACTING BETWEEN THE UPPER END OF SAID VESSEL AND SAID BASE AND HOLDING SAID MALE SURFACE OF SAID LOWER OPEN END OF SAID VESSEL 